The Study Of Experiments And Reaction Kinetic Mechanism On The Ignition Of C₁-C₃ Diluted With N₂ And CO₂

Lean combustion with high efficiency and low pollution and oxy-fuel combustion with effectively capturing CO₂ are promising advanced combustion technologies to deal with global warming.Dilution is the common feature of the two combustion modes,and it is the key to achieve high efficiency and low pollution combustion.Because dilution will also cause problems in fuel ignition and combustion stability,the mechanism of dilution effect on ignition is an important basic content in the above combustion research,and also one of the hot issues in current research.Firstly,the ignition temperature of CH₄ diluted with N₂ was measured on a self-made counterflow configuration.Through the evaluation of mainstream mechanisms,it is found that these mechanisms can not predict the experimental ignition temperature well.A modified mechanism has been proposed by substitution of the news channels of CH₃+O and CH₂+O₂ for the corresponding channels in USC Mech 2.0.The modified mechanism has been verified by present experiments and other experiments under the intensely diluted CH₄ condition.When CH₄ is intensely diluted by N₂,CH₂+O₂(?)CO+OH+H,CH₃+O(?)CO+H+H2,and CO+OH(?)CO₂+H,which have little effect on conventional ignition,play an "extra" role in the ignition of CH₄ and promote the ignition.The results show that the main oxidation chain of CH₃ extends to CO₂.Secondly,the ignition temperature of CH₄ intensely diluted with CO₂ in O₂/CO₂ atmosphere was measured.The experimental results show that for the same fuel dilution concentration,the higher the O₂ concentration in O₂/CO₂ atmosphere,the lower the ignition temperature.The difference of ignition temperature of CH₄ caused by O₂ concentration in the oxidant will decrease significantly with the decrease of CH₄ concentration,but the difference is not obvious when the fuel is intensely diluted to 9%.The updated mechanism,IDIM(intensive dilution ignition mechanism),can well predict the ignition temperature of CH₄ in O₂/CO₂ atmosphere with different O₂ concentration oxidants and the experiments of Fotache et al.When the O₂ concentration in the oxidant is very high and the fuel is intensely diluted,the path,CH₃?CH₃O?CH₂O,plays an important role in the ignition When CH₄ is intensly diluted to 9%,the ignition temperature of intensely diluted CH₄ is mainly determined by the fuel concentration.The chemical and physical properties of CO₂ inhibit the ignition,and the former is the main reason that the ignition temperature of CO₂ is higher than that of N₂ dilution.Then, the ignition temperature of C₂H₆ intensely diluted with N₂ was measured when the O₂ concentration range of the oxidant was 10%,21%,30% and 40%.The experimental results show that the ignition temperature of C₂H₆ increases with the increase of O₂ concentration when O₂ concentration in O₂/N₂ atmosphere is from 21% to 40% and the fuel concentration is the same.For 7% C₂H₆,the order of ignition temperature from low to high is 21% <10% <40%.For 20% C₂H₆,the order of ignition temperature from low to high is21% <40% <10%.The main effect of dilution on the ignition of C₂H₆ is that CO+OH(?)CO₂+H becomes important under the condition of intense dilution.Through the S-curves analysis,the present of the “slow" radical concentration is not the important indicator of the effect of dilution on the ignition of C₂H₆.When C₂H₆ is intensely diluted(7%C₂H₆),the chemical reaction heat of the reactions which have a great influence on ignition causes the difference of ignition temperature at different oxygen concentration.At last,the ignition temperature of C₁-C₃ alkanes intensely diluted with N₂ and CO₂ in O₂/N₂ atmosphere was measured.The experimental results show that the ignition temperature of C₁-C₃ alkanes diluted with CO₂ is higher than that diluted with N₂ at the same fuel concentration.The main reason is the high specific heat of CO₂ compared with N₂.When the C₁-C₃ is intensely diluted by CO₂ and N₂,CO+OH(?)CO₂+H can significantly promote the ignition of C₁-C₃ alkanes,which is the common feature of dilution effect on fuel ignition.The reaction mechanism,IDIM 2.0R,proposed in this paper has been proved to be suitable for the ignition of C₁-C₃ alkanes under dilution conditions through ignition temperature,ignition delay time and flame propagation speed.